WASHINGTON (AP) — It’s double trouble for the National Zoo after its adult female panda gave birth to twins. In addition to Bao Bao, Mei Xiang and the new cubs, the zoo is also home to an adult male panda named Tian Tian. Zoo director Dennis Kelly said at an evening news conference following the first cub’s birth that he was “so happy, so pleased, so excited.” Fans who want to see the newest pandas will have to try to catch a glimpse of them on the zoo’s online panda cameras. Though the zoo’s camera-viewing site can host about 850 viewers at a time, spokeswoman Pamela Baker-Masson says the site has been overloaded with people trying to watch. Mei Xiang was artificially inseminated with sperm from Tian Tian and a panda named Hui Hui from Wolong, China, who was determined to be one of the best genetic matches. The zoo will use saliva from the cubs’ mouths to determine gender and paternity, said Laurie Thompson, a giant panda biologist at the zoo.